The present invention relates to the selective application and removal of particular coatings from metal parts, particularly metallic parts used as structural components in aircraft, space vehicles, or the like.
Occasionally, it is necessary to remove a lacquer coating, a paint coating or a varnish coating from the outer skin of an aircraft. The purpose thereof is to inspect the integrity of the metallic substrate underneath, or simply for purposes of re-varnishing or re-painting the part. The known methods for removal of varnish paint and lacquer are very expensive. Moreover, it was found that the removal unduly loads the ecology because the removing liquids are relatively poisonous and, in cases, evaporate rather rapidly. See, as to this aspect, the German printed patent application No. 25 19 559.
Some aircraft manufacturer and operators (airlines) have, therefor, opined that they should use their aircraft essentially without any unique, for exampel, airline- specific coating. This is an intriguing aspect, because it leads to considerable savings in weight which, of course, is beneficial on the positive side, as far as payloads are concerned. However, the avoidance of varnishing, painting or lacquer coating an aircraft is little more than wishful thinking, because it can, in fact, be realized only with considerable expenditure. The reason for this is that these metal parts have been anodized by chromic acid, and prior to being assembled, for example, through some bondung and adhesive technique, they are always provided with a primer. This primer will then serve as a base coating for any possible subsequent varnishing, painting or lacquering. However, the aircraft operator may acquire an aircraft which he does not want to have provided with a lacquer, paint or varnish coating, or the aircraft operator may want only some parts to be so coated. Therefore, in such a case, the outer skin has to be subjected to a primer removal process which, of course, takes place after the aircraft has been assembled. The removal of the primer can be obtained, for example, through blasting, grinding, followed by subsequent polishing, but it is immediately apparant that these kinds of removal process may locally produce damage in the metal structure. This damage may be unexpected and, in fact, appear, in some form, as a hidden defect. Independently from the safety factor involved here, this removal process is labor extensive, and, therefore, expensive.